On Tue, Jan 05, 2021 at 10:04:58AM +0000, John Garry wrote:
> On 05/01/2021 02:20, Ming Lei wrote:
> > On Mon, Jan 04, 2021 at 10:41:36AM +0000, John Garry wrote:
> > > On 27/12/2020 11:34, Ming Lei wrote:
> > > > In case of blk_mq_is_sbitmap_shared(), we should test QUEUE_FLAG_HCTX_ACTIVE against
> > > > q->queue_flags instead of BLK_MQ_S_TAG_ACTIVE.
> > > >
> > > > So fix it.
> > > >
> > > > Cc: John Garry<john.garry@xxxxxxxxxx>
> > > > Cc: Kashyap Desai<kashyap.desai@xxxxxxxxxxxx>
> > > > Fixes: f1b49fdc1c64 ("blk-mq: Record active_queues_shared_sbitmap per tag_set for when using shared sbitmap")
> > > > Signed-off-by: Ming Lei<ming.lei@xxxxxxxxxx>
> > > Reviewed-by: John Garry<john.garry@xxxxxxxxxx>
> > >
> > > > ---
> > > > block/blk-mq.h | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/block/blk-mq.h b/block/blk-mq.h
> > > > index c1458d9502f1..3616453ca28c 100644
> > > > --- a/block/blk-mq.h
> > > > +++ b/block/blk-mq.h
> > > > @@ -304,7 +304,7 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
> > > > struct request_queue *q = hctx->queue;
> > > > struct blk_mq_tag_set *set = q->tag_set;
> > > > - if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &q->queue_flags))
> > > > + if (!test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
> > > I wonder how this ever worked properly, as BLK_MQ_S_TAG_ACTIVE is bit index
> > > 1, and for q->queue_flags that means QUEUE_FLAG_DYING bit, which I figure is
> > > not set normally..
> > It always return true, and might just take a bit more CPU especially the tag queue
> > depth of magsas_raid and hisi_sas_v3 is quite high.
>
> Hi Ming,
>
> Right, but we actually tested by hacking the host tag queue depth to be
> lower such that we should have tag contention, here is an extract from the
> original series cover letter for my results:
>
> Tag depth 4000 (default) 260**
>
> Baseline (v5.9-rc1):
> none sched: 2094K IOPS 513K
> mq-deadline sched: 2145K IOPS 1336K
>
> Final, host_tagset=0 in LLDD *, ***:
> none sched: 2120K IOPS 550K
> mq-deadline sched: 2121K IOPS 1309K
>
> Final ***:
> none sched: 2132K IOPS 1185
> mq-deadline sched: 2145K IOPS 2097
>
> Maybe my test did not expose the issue. Kashyap also tested this and
> reported the original issue such that we needed this feature, so I'm
> confused.
How many LUNs are involved in above test with 260 depth?
Thanks,
Ming
